Nonlinear Photoelectric Properties by Strained MoS₂ and SnO₂ Core-Shell Nanotubes for Flexible Visible Light Photodetectors

A new type of coaxial hetero-structured MoS₂/SnO₂ nanotube (MS-NT) array is rationally designed for flexible visible light photodetector. Herein, a suitable solution for fabricating MS-NT comprising SnO₂ with controlled thickness and strain is proposed. The thickness of SnO₂ deposited on MoS₂ nanotubes are delicately manipulated by adjusting atomic layer deposition (ALD) cycles, which cause the internal tensile strain of the hybrid nanotubes. The photocurrent of the MS-NT-based photodetector exhibits high photoresponsivity values of 198.4 mA W^-1 and external quantum efficiency of 0.78%. In the analysis, a linear correlation between the excitation power and the photocurrent extracted from the MNT-based devices is discerned. At the same time, a superlinearity of photocurrent in the MS-NT arrays-based device is found. Density functional theory calculations are adopted to unveil the strong correlation between the strain, bandgap, and photocurrent of the MS-NT, which is a decisive factor for understanding the experimental evidences. The detailed mechanism for enhance photoresponsivity is further suggested for the strain-tailored MS-NT arrays-based device. Such peculiar properties are expected to open a new chapter in the era of smart optical devices that require low driving voltage and high power efficiency.